Abstract: An improved billet and process for producing a tubular body by forced plastic deformation is disclosed. The billet includes a metallic tubular sheath, a metallic center core and a salt intermediate core. The radial thickness of the metallic tubular sheath is equal to or less than 0.11 times the outer diameter of the metallic tubular sheath. The metallic center core is positioned within the tubular sheath and is surrounded by the salt intermediate core which fills the cylindrical space between the tubular sheath and the center core. In the process of the present invention, the foregoing billet is subjected to forced compulsory deformation to reduce the diameter of the billet. Thereafter, the intermediate core is removed through solution and the center core is drawn out of the sheath in order to obtain the tubular body.

Abstract: Through employment of a core-and-sheath construction having a number of axially elongated indentations along the border for the billet with the core of an easily soluble material, extrusion such as hydrostatic extrusion can advantageously be utilized for production of heat pipes with enhanced precision and operational efficiency in process. Indentations, which work as a wick in the heat pipe, may be provided by forming axially elongated grooves either in the inner peripheral surface of the sheath or in the outer peripheral surface of the core.